Hitherto, in an air-conditioning apparatus, R410A being an HFC refrigerant has been mainly used as refrigerant to be filled into a refrigerant circuit. R410A has zero ozone depletion potential ODP, and hence does not cause depletion of the ozone layer. However, R410A has a property with a high global warming potential GWP. Therefore, in the aim of preventing the global warming, there has been an increasing shift from the HFC refrigerant having a high GWP such as R410A to an HFC refrigerant having a low GWP.
As such an HFC refrigerant having a low GWP, there is known, for example, halogenated hydrocarbon having a carbon double bond in composition. As representative examples, there are known HFO-1234yf (CF3CF=CH2; tetrafluoropropane), HFO-1234ze (CF3-CH=CHF), and HFO-1123 (CF2=CHF). Those are kinds of the HFC refrigerant. However, unsaturated hydrocarbon having a carbon double bond is called “olefin”, and hence those refrigerants are often expressed as HFO, with the initial letter “O” of olefin. Thus, those refrigerants are herein referred to as HFO refrigerants so as to be distinguished from the HFC refrigerants having no carbon double bond in composition such as R32 (CH2F2; difluoromethane) and R125 (CHF2-CF3; pentafluoroethane) forming R410A.
Such HFO refrigerant having a low GWP may be used in a form of a single-component refrigerant or in a form of a refrigerant mixture being a mixture with another HFO refrigerant. It is highly probable that the HFO refrigerant having a low GWP is used in a form of a refrigerant mixture with the HFC refrigerant as represented by R32. The HFO refrigerants or the refrigerant mixtures of the HFO refrigerant and the HFC refrigerant are not as highly flammable as an HC refrigerant such as R290 (C3H8; propane), but have mild flammability and are different from R410A being non-flammable. Therefore, caution needs to be taken with respect to a leakage of refrigerant. The refrigerant having flammability ranging from mild flammability to high flammability is hereinafter referred to as “flammable refrigerant”. R32 in a form of a single-component refrigerant has mild flammability like the HFO refrigerant. That is, R32 in a form of a single-component refrigerant is flammable refrigerant. Therefore, the refrigerant mixture of the HFO refrigerant and R32 is also the flammable refrigerant. R410A obtained by mixing R125 into R32 is non-flammable because of the property of R125.
When such flammable refrigerant leaks into an indoor space, and the leaked refrigerant stagnates without being diffused, there is a possibility of causing formation of a gas atmosphere having a flammable concentration. When any ignition source is present in the gas atmosphere having the flammable concentration, the refrigerant may catch fire. To avoid occurrence of such a situation of causing the leaked refrigerant to catch fire in the indoor space, it is necessary that the air-conditioning apparatus which uses the flammable refrigerant in the refrigerant circuit detect the leakage of refrigerant.
Hitherto, there has been proposed the following detection unit configured to detect the leakage of refrigerant in the air-conditioning apparatus. A temperature sensor is arranged at a position in the refrigerant circuit where liquid refrigerant may stagnate, for example, below a header of an indoor unit-side heat exchanger or at a liquid reservoir such as a receiver. When a refrigerant temperature detected by the temperature sensor falls at a rate exceeding a predetermined rate, a control unit determines that a leakage of refrigerant occurs (for example, see Patent Literature 1).
Further, there has been proposed the following air-conditioning apparatus. When a leakage of refrigerant is detected, an air-sending fan of an indoor unit is rotated to diffuse the leaked refrigerant in the indoor space, thereby preventing stagnation of the leaked refrigerant in the indoor unit or around the indoor unit. The working of air-sending of the air-sending fan causes diffusion of the leaked refrigerant, thereby preventing formation of a gas atmosphere of the leaked refrigerant gas having a flammable concentration (for example, see Patent Literature 2).